The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
To reduce the quantity of undesirable particulate matter and NOx emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment systems have been developed. The need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented.
One method used to reduce NOx emissions from internal combustion engines is known as selective catalytic reduction (SCR). SCR may include injecting a reagent into the exhaust stream of the engine to form a reagent and exhaust gas mixture that is subsequently passed through a reactor containing a catalyst capable of reducing the nitrogen oxides (NOx) concentration in the presence of the reagent. For example only, the catalyst may include activated carbon or metals, such as platinum, vanadium, or tungsten.
An aqueous urea solution is known to be an effective reagent in SCR systems for diesel engines. However, use of an aqueous solution and other reagents may have disadvantages. Urea is highly corrosive and may attack mechanical components of the SCR system. Urea also tends to solidify upon prolonged exposure to high temperatures, such as encountered in diesel exhaust systems. A concern exists because the reagent creates a deposit that is not used to reduce the NOx.
Urea injection systems for the treatment of diesel engine exhaust vary substantially in that different original equipment manufacturers (OEMs) specify reagent injectors having different ranges of injection flow rates. When reviewing several different OEM specifications together, the entire range of reagent injection flow rates to be provided may be expansive. As such, manufacturers of reagent injectors presently provide several different injectors each having a similar total flow rate range but sized such that the maximum and minimum values are spaced apart from one another.
A reagent injector includes a pintle that actuates axially within the reagent injector to open and close the reagent injector. A solenoid coil of the reagent injector produces a magnetic field based on current flow through the solenoid coil. The pintle compresses a return spring based on the magnetic field to open the reagent injector. When the magnetic field collapses, the return spring biases the pintle to close the reagent injector.
The pintle, however, may become magnetized over time. If the pintle becomes magnetized, the reagent injector may close at a slower rate. Additionally, current flowing through the solenoid coil generates heat. As described above, the reagent may react negatively to heat. As such, a need exists to minimize heat generated for opening a reagent injector. A need also exists to minimize a probability of the pintle becoming permanently magnetized.